Regulation of the synthesis of two specific liver enzymes by hormones and cyclic AMP (cAMP) analogs is being studied in cultured hepatome (H35) cells as a model system. Previous evidence has suggested that the synthesis of both proteins is regulated by cAMP analogs at the level of translation. Current studies are aimed at determining which step in the translation process is subject to regulation. Ribosomal transit time measurements using radioimmunochemical methods will be made initially for one of the two proteins, tyrosine aminotransferase (TAT), in control-N6,O2' dibutyry cAMP (DBc) -or dexamethasone-treated H35 cells. Possible shifts in TAT polysome size after exposure of cells to DBc will be evaluated by incubating 125I-anti-TAT FAb fragments with sucrose gradient fractions. Analysis of the possible stimulation of ribosome or polysome - associated protein phosphorylation by DBc in intact cells will be undertaken. In addition, the possible role of phosphorylation of nascent TAT chains in the action of cAMP analogs on TAT synthesis will be explored. Finally, various clones of H35 cells and somatic cell hybrids between H35 cells and normal liver cells will be analyzed for their patterns of response to DBc and Dex.